1. Field of the Invention
This invention relates to an invention for draining blood from the right atrium of a heart and more specifically relates to a relatively rigid two stage venous cannula with an angled bend and a drainage hole located at the apex of the bend.
2. Description of Related Art
During cardiac surgery, it is often desirable to maintain circulation of blood through a patient's body. This is often done by connecting a patient to an extra-corporeal system that adds oxygen to and removes carbon dioxide from the blood, heats or cools the blood and provides impetus to the blood to cause the blood to circulate through the patient's vascular system.
It is necessary to connect the patient to the extra-corporeal circuit. This is usually done by inserting cannula into the patient's venous system near or in the heart to remove blood from the patient and direct it to the extra-corporeal circuit. After the blood has passed through the extra-corporeal circuit, the blood in infused into the patient's arterial system near the heart.
One way of removing venous blood from a patient is shown in FIG. 1. Two single-stage cannulae 2,4 are used. Both cannulae 2,4 are right-angle cannulae with a distal end 6,8 respectively. Each cannula 2,4 has openings 10,12 at the distal end 6,8, respectively.
Cannula 2 is placed in the patient's superior vena cava 14 through an opening 16 in the superior vena cava 14. The distal end 6 is directed away from the heart 18 so that opening 10 removes blood moving toward the heart 18 through the superior vena cava 14.
In like manner, cannula 4 is placed in the patient's inferior vena cava 20 through an opening 22 in the inferior vena cava 20. The distal end 8 is directed away from the heart 18 so that opening 12 removes blood moving toward the heart 18 through the inferior vena cava 20. Both cannulae 2,4 are joined together at a Y-connector (not shown) to form a single line of blood flow into the extra-corporeal circuit.
A disadvantage of this type of system is that two cannulae 2,4 must be used. In addition, two holes 16,22 must be placed in the patient's vascular system. It is preferable to use only a single cannula and to require only a single hole in the patient's vascular system, especially when the right atrium will not be surgically opened. Therefore, a two-stage cannulation system, such as is shown in FIG. 2, has been developed.
The previously known two-stage cannula 22 has openings 24 at the distal end 26 of the cannula and at least one opening 28 a distance from the distal end 26. In use, an opening 30 is made high in the patient's right atrium 32 and cannula 22 is inserted therethrough. The distal end 26 is advanced until it passes through the right atrium 32 and into the inferior vena cava 20. Opening 28 is located along cannula 22 so that opening 28 is located in the right atrium 32 when opening 24 is in the inferior vena cava 20.
In use, blood entering the right atrium 32 through the superior vena cava 14 is removed through opening 28. Blood flowing in the inferior vena cava 20 is removed through opening 24 before the blood enters the right atrium 32. Any blood entering the right atrium 32 from the inferior vena cava 20 is removed through opening 28. This allows a single two-stage venous cannula 22 to simultaneously drain the right atrium 32 and superior vena cava 14 through opening 28 while the inferior vena cava 20 is drained through opening 24 at the distal end 26 of cannula 22.
The two-stage venous cannula was introduced by Sarns, Inc. of Ann Arbor, Mich. to the cardiac surgery market in the late 1970's as an alternative to bi-caval venous cannulation on procedures for coronary artery by-pass grafts (CABG). U.S. Pat. No. 4,129,129, issued to Bruce A. Amrine on Dec. 12, 1978 and U.S. Pat. No. 4,639,252 issued to Michael N. Kelly, et al. on Jan. 27, 1987 disclose two-stage venous cannulae.
These previously known two-stage cannulae have been made of flexible material so that the cannula may bend as needed to be placed into and remain in the patient's inferior vena cava 20 and right atrium 32. A problem with such a cannula is that because of the flexible nature of the cannula, it is often difficult to insert, advance and position the cannula as desired.
An additional problem with previously known cannulae is that the cannulation site is located in the right atrium. This places the cannula near the aorta. Having the cannula near the aorta is potentially troublesome because the cannula may block visibility and access to areas of surgical interest in the heart.